Ed Miliband risks political isolation in office and a rapid loss of legitimacy similar to that suffered by François Hollande in France unless he does more now to build support for a radical programme of change, according to the leftwing campaign group Compass.

A new pamphlet by Compass – entitled Future Shock – adds to the pressure on the Labour leader, who has suffered a difficult 10 days, including the pomp of the Conservative commemoration of Lady Thatcher, criticism from the political figure who still looms large over his own party, Tony Blair, and a worsening performance in the polls.

The concerns outlined by Compass reflect concern on the political left that the Labour leader has not been explicit enough about what he will do in office if he is to claim a solid mandate for reform.

It urges him to look at how President Barack Obama ran for his second term on a programme of a fairer social distribution of spending cuts and tax increases. It also urges Miliband's office to recognise that it may need to work with the Liberal Democrats in government and that links should be built now.

The report says: "A weak government that will need to strengthen its position might instead find itself floundering fast."

Compass warns that Miliband has not yet fully formed the foundations for the popular support for his policies that would be needed to resist the probable intense opposition from banks, business, European partners, parliament and even the unions.

The latest advice comes after interventions by Blair – the former prime minister called for more policy specifics – and a new Ipsos Mori poll showing that only 29% of respondents believe Labour is ready to form a government, down 2% on a year ago. An ICM poll for the Guardian this week put Miliband at his lowest leadership rating since he became leader, but other polls show Labour enjoying mainly robust double digit leads.

Blair cautioned Miliband not to presume that the centre ground was moving to the left, or to think it was feasible to shift the centre ground from opposition. He said it would be fatal for Labour to become simply the curator of the status quo.

But in one of their bolder strategic moves, Miliband and his allies have firmly rejected much of the advice given by Blair; in so doing, the Labour leader has confirmed that he will govern from the left with a new approach.

Some Blairities do not oppose the specifics emerging from Miliband's team on regional banks or training, but say it is not enough. One Labour thinktank chief said: "I don't think it is sustainable to go on like this. If we maintain a double digit lead, the media will turn its attention to us, and we cannot just say we are reviewing everything. From next autumn conference we will be in election campaign mode, but at present we are talking about 'earning and belonging'. You cannot put that on a pledge card."

Certainly it would be a tough call for Sir Jeremy Heywood, the head of the civil service, to turn the abstractions of "Blue Labour" thinker Lord Glasman into Miliband's first legislative programme.

Similarly, Labour websites are full of rhetoric about tough spending choices after 2015 but, with the exception of a Fabian review of spending, very few examples of a tough choice. On the critical issue of whether to follow the coalition's deficit reduction programme when it is announced this summer, there is disagreement. The Blairite thinktank Progress says yes. Others such as Unite have said no.

Shadow chancellor Ed Balls would probably favour a late call months before the general election. The argument for that course is clear. Premature fiscal commitments can come back to haunt an opposition, as they did for John Smith in 1992 and David Cameron 2009. Jon Cruddas, the head of Labour's policy review, told a One Nation conference now was not the time for policy, saying that would be to put the cart before the horse. Indeed, there are few political leaderships that have put so much faith in the importance of ideas.

Miliband will on Friday draw an explicit parallel with the way Margaret Thatcher also valued ideas in politics.

In a speech in Scotland he will argue: "Back in the 1970s, it was clear the country needed a new way of doing things – a new settlement – and so too today. The old way of running our economy just doesn't work any more: deregulation; the dominance of finance over industry; allowing large private-sector vested interests to flourish; government getting out of the way in the economy; the promise that the majority would always do well from an in-it-for-yourself, laissez faire, deregulated economy just isn't working for most working people."

He went even further in expressing his faith in ideas in an interview published on the Shifting Grounds website.

He said: "I now see clearly what the pieces of this are. It's about a proper skills system, a proper banking system, an industrial policy, tackling short-termism, infrastructure. It's about a suite of things, some of which they have in parts of the continent, some of which they have in parts of Scandinavia, that come together and form a body of ideas around responsible capitalism. I think it's absolutely where the public is.

"People sometimes say that I'm too interested in ideas, predistribution and all those sort of wonky things. Of course you've got to make the ideas mean something at the kitchen table, but getting the ideas right, the intellectual foundations, is absolutely crucial. And they're particularly crucial in tough times. It's easier in good times. But in tough times you've got to have a robust sense of where you stand."

Compass – which has close links to Miliband's office – suggests that due to the economic circumstances "Labour cannot expect anywhere near the quality or quantity of support it enjoyed when it came to office in 1997" in a wave of revulsion at Conservative rule.

The author of the Compass report, Dr Matthew Sowemimo, says: "Thatcher came to office in 1979 with ideological winds at her back. Her case that the state had become too dominant and that trade union power needed to be curbed seemed plausible given the industrial strife of the winter of discontent.

"There has yet to be a comparable intellectual ferment around responsible capitalism or reformed social democracy. There are some isolated thinkers on topics like pre-distribution but there are no unifying precepts that can guide the direction of policy across the board. If anything the electoral consensus in support of free market policies has proved to be surprisingly resilient in the face of the banking crash of 2008."

The paper warns: "Recent years have shown a marked shift away from public support for the redistribution of wealth and particularly for welfare spending. British Social Attitudes data showed this shift began when Labour was in office and occurred primarily due to Labour voters becoming more hostile to welfare spending."

Miliband recognises that his mettle is now going to be tested as never before, but will not change the pace at which he plans to offer the country a very specific programme. He has been proved right on many big judgments in his leadership so far, so it is quite possible that his many internal dissenters will be proved wrong on this.